INSECTICIDES ON GARDEN AND GREENHOUSE PESTS. 753 



as the Pear-tree " slug worm." About the beginning of the second week 

 in June the moths begin to appear, and a week later very few remain to 

 hatch from the chrysalis. Immediately prior to the escape of the moth, 

 the chrysalis bursts through the bonds of silk forming its frail cocoon, 

 and works the anterior portion of its body to the outside of its retreat. 

 The pupal skin then bursts and liberates the imprisoned moth, while the 

 empty skin remains behind (fig. 318, 2a), anchored to the silken cocoon 

 by means of hooked bristles with which the tail is furnished. 



Fig. 318. — Fkuit-tree Tortrix {Penthina variegana). 



(1) Caterpillar ; (2, 2a) chrysalis ; (3, 3a) perfect insects at rest, natural position, 

 and with the wings expanded ; (4) chrysalis hidden between two leaves spun together 

 — the upper leaf is cut open and pinned back to show the chrysalis ; (5) edge of leaf 

 turned down by caterpillar ; (6) winter galleries or cocoons in which the young cater- 

 pillars hibernate. (All actual size.) 



The full-fed caterpillar (fig. 318, 1) is about five-eighths of an inch long 

 (16 to 19 mm.), and rather stout ; the colour is leaf-green above, with a 

 rather indistinct bluish dorsal line, with the head and first segment 

 intense, shining black, underside paler ; and there are numerous fine 

 hairs scattered over the body. 



The chrysalis (fig. 318, 2, 2a) is at first of a pale greenish colour, but 

 soon changes to a uniform dull black. 



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